ASA 124th Meeting New Orleans 1992 October

1pPP7. Across frequency grouping in the binaural masking release of
complex sounds.

John F. Culling

Quentin Summerfield

MRC Inst. of Hear. Res., University Park, Nottingham NG7 2RD, UK

Common periodicity has been proposed as a basis for segregating concurrent
sounds that differ in fundamental frequency. Common interaural time delay may
play an analogous role in segregating complex sounds whose sources differ in
spatial position. To explore this analogy, masked identification thresholds
were measured for synthesized vowels in pink noise in several binaural
conditions. The across-frequency coherence of each sound's interaural phase
relationships was manipulated. The results were interpreted in terms of an
interaural cross-correlation mechanism that groups components that produce
cross-correlation maxima at the same delay. Masking release (compared to the
condition where both noise and vowel were in phase at each ear) was found to
depend mainly upon the coincidence across frequency, at the same correlation
delay, of cross-correlation maxima due to the noise. Masking release was
largely independent of the pattern of interaural correlations generated by the
target vowel, providing the pattern differed from that of the masking noise.
The result is analogous to the demonstration that the periodicity of maskers,
not target vowels determines ease of segreagation based on differences in
fundamental frequency, and shows that the binaural masking release of complex
sounds includes an across-frequency grouping mechanism.